[Brian]

OmniFocus stores the information about what columns are visible on a per-perspective basis. If you're seeing those columns some of the time and not seeing them at other times, this is likely why.

The fix for this has two parts; each is optional, depending on what you'd like your setup to be. First, you can set the baseline behavior - "show these columns, and hide these ones, unless my perspective tells you differently." Then, you can go ahead and save perspective-specific overrides to the default behavior into your various perspectives. Instructions for both approaches follow.

Setting the default behavior

1. Open OmniFocus
2. Select Perspectives -> Revert to Default View
3. Select View -> Show View Bar (if the menu item reads "Hide View Bar", skip this step.)
4. Control-Click the white column headers that appear just beneath the view bar. A contextual menu will appear with three choices: Estimate, Start Date, and Due Date. If you select an item from the context menu, the corresponding column will become visible.
5. Quit OmniFocus to make sure we save this change to your preferences.

Setting the behavior in a specific perspective

1. Open OmniFocus
2. Select the perspective you want to edit from the Perspectives menu.
3. Select View -> Show View Bar (if the menu item reads "Hide View Bar", skip this step.)
4. Control-Click the Column headers. A contextual menu will appear with three choices: Estimate, Start Date, and Due Date. If you select an item from the context menu, the corresponding column will become visible.
5. Select Perspectives -> Take Snapshot of Perspective. You should be good to go at this point.

Hope this helps!

Edit: for the 2nd time in 2 days, changed "command-click" to "control-click". No cookie for Brian!